Japanese Patent Laying-Open No. 58-110099 (PTD 1) describes an apparatus for preventing an electronic device from overturning. In the apparatus described in this document, units are mounted in a housing and each unit can be pulled out from a front side. A guide rail configured to move in a front-back direction along with each unit is attached to each of right and left side surfaces of the unit, and sliding between this guide rail and a fixed rail fixed to an inner wall of the housing enables the unit to move in the front-back direction.
As for a power supply apparatus, there is a type of power supply apparatus having a plurality of units mounted in a housing, and each unit may be pulled out from a front side by an operator.